The present invention is directed to an imaging process. More specifically, the present invention is directed to an imaging process wherein images are generated on a transparent receiver sheet that is positioned in the imaging apparatus by infrared sensors that detect the presence of an infrared absorbing material situated in a specified location on the receiver sheet. One embodiment of the present invention is directed to a process which comprises providing an imaging apparatus equipped with a path for moving receiver sheets through the apparatus and having infrared sensors situated along said path, incorporating into the imaging apparatus a substantially transparent receiver sheet having coated on at least a portion thereof an infrared absorbing material contained in a polymeric binder, passing the substantially transparent receiver sheet along the path, wherein the infrared sensors detect the presence of the infrared absorbing material on the substantially transparent receiver sheet, and generating an image on the substantially transparent receiver sheet.
Apparatus and processes for sensing and positioning receiver sheets in imaging systems are known. For example, one type of paper sensing device takes the form of switches activated by switch arms located in the path of movement of the receiver sheet. Other sheet detection systems use photodetectors combined with light sources for sensing sheet presence or absence. It is often necessary to provide light baffles or other enclosures to ensure that the machine photosensitive surface does not come into light contact with the light sources of the sensors. U.S. Pat. No. 3,684,890 (Hayne et al.), the disclosure of which is totally incorporated herein by reference, discloses a misfeed detector for sensing the presence of a properly fed sheet of support material prior to the sheet being conveyed to the photoconductive surface of a xerographic machine for transfer of a developed image thereto. A photocell system utilizes two reflections from an area where both a sheet should be located and a gripper member is situated to determine whether a sheet is correctly positioned to be conveyed for an image transfer. If a misfeed of the sheet is detected by the photocells, a shutdown of the xerographic machine is effected. In addition, U.S. Pat. No. 3,882,308 (Daughton et al.), the disclosure of which is totally incorporated herein by reference, discloses a multiple sheet detecting system for use in a sheet feed path to provide a signal to a machine control when superposed sheets are fed past a detection station. The detection system has a source of illumination and photosensitive elements at the detection station. Illumination is interrupted by the presence of a sheet or sheets in the sheet path and also by a sample sheet such that a comparison is made between the sample and fed sheets. An electronic circuit coupled to the photosensitive elements which experience a change in resistance depending on the transmittance of a sheet or sheets in the sheet path generates an output signal when there is a multiple sheet condition. Also of interest with respect to photodetection devices is U.S. Pat. No. 3,932,755, the disclosure of which is totally incorporated herein by reference. Yet another system, as disclosed in, for example, U.S. Pat. No. 4,513,404 (Huggins), the disclosure of which is totally incorporated herein by reference, employs a single sensor transmitter and receiver connected to a pneumatic bus. The pneumatic bus includes a plurality of sensor locations or ports disposed at various points along the paper path in the imaging apparatus. The acoustic impedance characteristic at each port is modified by the absence or close proximity of a sheet of paper.
While most images are generated on opaque paper receiver sheets, it is frequently desirable to produce images on transparent receiver sheets so that the image can be projected in a magnified fashion to a screen for viewing by a large number of people. Difficulties are frequently encountered in attempting to feed transparent receiver sheets automatically through processing stations in imaging apparatuses because most machines employ photosensors or photodetectors to monitor the passage of receiver sheets through the machine. Since the transparency is transparent, it is not seen at particular places in the machine by the photosensors and photodetectors; accordingly, its progress is not satisfactorily monitored, and the timing of the various processing operations may then be inappropriate to the location of the transparency, resulting either in an imperfect or in a machine malfunction.
One technique that has been employed to solve this problem is to modify the transparent film by printing or coating an opaque material on a sheet in a location that will pass over the photosensors in the machine. Typically, this technique entails the use of a relatively narrow opaque strip along one edge of the transparent receiver sheet which permits the transparent film to run through a variety of machines with photosensors in different locations relative to the transparent sheet. This technique, however, suffers from the difficulty that placing the opaque stripe over the entire leading edge of the transparent film provides an opaque area that projects as black, and thus effectively limits the area of the transparency available for projection.
Another technique for solving this problem entails attaching a sheet of paper, plastic, or like material to the back of the transparent receiver sheet with a tape or an adhesive that permits easy removal of the opaque sheet before projection and after preparation of the image on the transparency. While this technique solves the photosensor problem, it also has several difficulties. Frequently, the adhesive or the tape used to affix the paper backing is incompletely removed from the transparent film with the paper backing sheet and the residual adhesive is visible on the projection, thus detracting from the viewing quality of the transparency. When the backing sheet is paper, it often expands and contracts its dimensions with changes in moisture from varying humidity conditions; this dimensional instability of the backing sheet relative to the more stable transparency film may give rise to composite curl that makes feeding difficult or creates wrinkles or jams as the sheet is processed in the machine. Finally, because the backing sheet may be attached only along one edge, the composite sheets are susceptible to mechanical separation by the forces associated with the feeding system of the machine. Separation can result in severe wrinkling of the paper or machine jams. In addition, a composite sheet of this type will not be suitable for use in machines employing multifeed detectors employing thickness sensors. The increased thickness of the composite sheet is sensed as a double sheet feed, and the sheet is aborted or the machine shuts down. Further, the low thermal conductivity and the relatively high thermal insulating property of the paper may prevent some of the available fusing energy from reaching the image when the transparency passes the fuser section of imaging apparatuses employing heat fusible toners to develop the image, thus resulting in inadequately fused images.
Examples of documents disclosing the aforementioned techniques for generating images on transparencies include U.S. Pat. No. 3,618,752, U.S. Pat. No. 3,519,124, U.S. Pat. No. 4,051,285, U.S. Pat. No. 3,944,710, U.S. Pat. No. 3,949,148, Japanese Patent Publication 57-76554A, and Japanese Patent Publication 57-122448, the disclosures of each of which are totally incorporated herein by reference.
The process of the present invention enables feeding of transparent receiver sheets through imaging apparatuses employing photodetectors or photosensors with none of the above disadvantages.
U.S. Pat. No. 4,808,565 (Whitcomb et al.), the disclosure of which is totally incorporated herein by reference, discloses thermographic materials that are colorless when unexposed but provide an intense dark image when thermally addressed. The materials comprise a transparent binder and at least two thermal reactants that react with each other at elevated temperatures. One of the reactants is in solid solution in a binder and the other is dispersed in microparticulate form in the binder. The materials can be used as coating and drying layers on a substrate such as sheets. The sheets give thermal images exhibiting good discrimination when examined with near-infrared radiation.
U.S. Pat. No. 4,816,386 (Gotoh et al.), the disclosure of which is totally incorporated herein by reference, discloses a near-infrared sensitive phthalocyanine polymer composition that comprises a substituted aluminum phthalocyanine and a polymer wherein substituted aluminum phthalocyanine dimers and/or dimer aggregates which are responsible for the near-infrared sensitivity are included. The compositions have optical properties which are capable of being chemically fixed. The compositions can be used for an optical information recording medium on which information can be recorded.
U.S. Pat. No. 4,853,362 (Satake et al.), the disclosure of which is totally incorporated herein by reference, discloses a heat sensitive recording material with a support and a color developing layer which comprises both as a colorless basic chromogenic dye at least one of a particular fluorane-type leuco dye and a particular divinyl compound and as a stabilizer a particular halogen substituted zinc benzoate derivative. The heat sensitive recording material exhibits optical readability in the near infrared region.
U.S. Pat. No. 4,553,033 (Hubble, III et al.), the disclosure of which is totally incorporated herein by reference, discloses an infrared sensor. More specifically, this patent discloses an integral compact infrared reflectance densitometer including a substrate supporting an LED, a control photodiode to compensate for component degradation, a background photodiode to compensate for background radiation, and a large area photodiode to provide an electrical signal representative of the amount of toner particles on the photosensitive surface. Also carried on the substrate is a field lens to focus light rays reflected from the photosensitive surface onto the signal photodiode. The substrate is precisely secured to a molded housing having integral collector and collimating lenses. Four extending pins on the housing engage four apertures on the substrate to locate the substrate with respect to the housing and align the LED and field lens carried on the substrate with the collector and collimating lenses of the housing. Also carried on the substrate is an aperture box to permit a portion of the LED light to project through the collimating lens to the photosensitive surface and a portion of the light to be reflected onto the control photodiode to control light output. The light rays reflected from the photosensitive surface are gathered in a collector lens and projected through the field lens to be focused onto the signal photodiode. An L-shaped clip and an appendage with an elongated aperture extend from opposite ends of the housing to position and align the infrared reflectance densitometer in the reproduction machine with respect to the photosensitive surface.
While known compositions and processes are suitable for their intended purposes, a need remains for processes for generating images on substantially transparent receiver sheets. In addition, a need remains for processes for using substantially transparent receiver sheets in imaging apparatuses that employ optical detection systems for determining the position of receiver sheets in the apparatus. Further, there is a need for processes for generating images on substantially transparent receiver sheets in imaging apparatuses that employ optical detection systems wherein the receiver sheet has no opaque portion, such as a strip, for the purpose of optical detection. Additionally, a need remains for processes for generating images on substantially transparent receiver sheets in imaging apparatuses that employ optical detection systems wherein the receiver sheet has no opaque additional sheet attached thereto. A need also exists for imaging processes with substantially transparent receiver sheets with maximized printing area in which the printed image can be situated for optical projection onto a screen. There is also a need for processes for generating images on substantially transparent receiver sheets in imaging apparatuses wherein the substantially transparent receiver sheets are coated in substantially the same location on all four edges with an infrared absorbing material contained in a polymeric binder, thereby enabling the sheet to be fed through the apparatus in any orientation. Further, there is a need for processes for generating images on substantially transparent receiver sheets in imaging apparatuses wherein the substantially transparent receiver sheets are coated with an infrared absorbing material contained in a polymeric binder in an encoded pattern and an infrared-sensitive scanning device in the apparatus detects and decodes the pattern and employs the information thus obtained to control registration of the image formed on the receiver sheet.